#include <iostream>
#include <vector>
#include <string>
using std::vector; using std::string; using std::cout; using std::endl; using std::cin;

int main()
{
	vector<string> scores = { "F", "D", "C", "B", "A", "A++" };

	int grade = 0;
	while (cin >> grade)
	{
		string lettergrade = grade < 60 ? scores[0] : scores[(grade - 50) / 10];
		lettergrade += (grade == 100 || grade < 60) ? "" : (grade % 10 > 7) ? "+" : (grade % 10 < 3) ? "-" : "";
		cout << lettergrade << endl;
	}


	return 0;
}